This invention relates generally to a vehicular power system and more particularly to a parallel hybrid system which utilizes an internal combustion engine in combination with an electric motor/generator (xe2x80x9cEMGxe2x80x9d) for applying torque to the drive train of a vehicle. An EMG control system manipulates and controls the contribution of torque delivered to the drive train from the EMG depending on conditions present in the operating environment of the vehicle and also controls the charging of a storage device by the EMG.
Vehicles such as automobiles and trains have long been powered by hybrid power systems. Such hybrid systems may include the combination of an internal combustion engine with an EMG to power the vehicle. In xe2x80x9cserialxe2x80x9d hybrid systems, an EMG or EMGs power the drive wheels of the vehicle while the internal combustion engine manipulates a generator for recharging an electrical power storage device (e.g., a battery, capacitor, flywheel, etc.) which in turn powers the EMG(s). In xe2x80x9cparallelxe2x80x9d hybrid vehicles, both the internal combustion engine and EMG may directly power the drive train of the vehicle. Typically, in most parallel hybrid designs, the drive train is powered either by the internal combustion engine alone or the EMG, but seldom together. Moreover, most parallel hybrid systems to date have been concerned primarily with reducing the emissions from the vehicle while still providing sufficient power for desired operation. In such vehicles, the EMG is utilized for start-up operations and relatively slow speed operation while the internal combustion engine is utilized for high speed operation.
U.S. Pat. No. 5,343,970 discloses the use of an EMG to provide assistance to the torque generated by the internal combustion engine in order to accelerate an automobile or to help power an automobile up a hill. U.S. Pat. No. 5,656,921 discloses the use of fuzzy logic as a control mechanism for a parallel hybrid powertrain.
The random application of EMG assistance is not efficient and may not be beneficial unless effectively controlled. The controlled application of EMG assistance is essential to ensure that the stability and overall performance of the hybrid vehicle may be maintained. Also, the haphazard application of EMG assistance may deplete the energy source thus preventing further EMG assistance from being available.
In applications such as highway driving, a vehicle must operate at relatively high speeds for long periods of time. Road racing in rallies presents even more extreme demands. For example, at the race held yearly in LeMans, France, high performance automobiles are required to operate continuously for twenty-four hours. The winner of the race is the automobile which has traveled the farthest in that time period. Consequently, the performance and durability of the power system, in addition to the effective management of race-restricted resources such as gasoline and tires, are essential to win such a race. In order for a hybrid automobile to operate in such an extended environment, the management of the power system is critical to ensure that the EMG assist capability of the EMG is utilized effectively, so that it will be available throughout the course of the race despite the limited capacity of any energy storage device. For example, the capacity of a storage battery is limited since the performance of the automobile is effected by its overall weight, and it is infeasable and counter-productive to have an overlarge battery system. Furthermore, it is desirable that in addition to providing additional torque, the EMG be able to operate at its optimum level enhancing the overall performance of the hybrid vehicle.
Thus, while hybrid systems have been known to operate vehicles, it is desirable to provide an EMG control system which may optimize and efficiently utilize the limited resources of the hybrid system under a variety of operating conditions. Also, since vehicles are utilized in many driving circumstances, it is desirable to provide a EMG control system which is adaptable to optimize performance for the current operating conditions of the vehicle.
Accordingly, it is an objective of the present invention to provide a parallel hybrid system which optimizes and efficiently utilizes an EMG to enhance the performance of a hybrid vehicle.
Also, it is an objective of the present invention to maximize EMG assistance and the regeneration of the power storage device when the surrounding operational parameters permit.
Additionally, it is an objective of the present invention to control the EMG assist and regeneration functions in a manner conducive to the operating environment.
It is also an objective of the present invention to provide a parallel hybrid system which is capable of providing the performance characteristics necessary for winning road races, such as The Twenty-four Hours of LeMans, by providing a smart control system for operating the EMG assist of an EMG.
In accordance with the invention therefore, a parallel hybrid power system is provided, including an internal combustion engine powered by fossil fuels. An EMG driven by an energy storage device (xe2x80x9cESDxe2x80x9d) is utilized for powering the vehicle. The ESD, in practice, could be a cell, a battery, a capacitor, a flywheel, or any of the means known to those skilled in the art for storage of energy. An EMG controller controls the amount of electrical current flow in both directions between the ESD and the EMG. A first set of demand parameters directs the EMG controller to control the amount of current which flows between the ESD and the EMG. This current may be utilized either to drive the EMG (xe2x80x9cEMG assistxe2x80x9d) or to recharge the ESD (xe2x80x9cregenerationxe2x80x9d). A set of limiting parameters representing the operating parameters of the system (e.g., battery temperature) are present for limiting the amount of demand of current between the EMG and the ESD. The limiting parameters may override or modify the effect of the demand parameters when predetermined operating conditions indicate that satisfying the requested demand of the demand parameters would jeopardize the operation of the vehicle.
Also, the vehicular power system may utilize other sets of demand parameters for manipulating the current flow between the ESD and EMG depending on the operational environment. This provides the vehicle with flexibility in different driving conditions.